[U-Boot] [PATCH 1/2] usb: kbd: allow multibyte sequences to be put into ring buffer

[Heinrich Schuchardt]

On 02/22/2018 03:20 PM, Marek Vasut wrote:
> On 02/22/2018 01:04 PM, Heinrich Schuchardt wrote:
>> The USB keyboard driver provides a ring buffer for key strokes.
>>
>> Function keys cannot be encoded as single bytes. Instead xterm control
>> sequences have to be put into the ring buffer.
> 
> Does it work without xterm or with any other terminal ?
I use two testing environments:

- USB keyboard and HDMI monitor. This does not involve xterm.
- Connection from Linux via serial cable. Linux screen or minicom
   transfer xterm escape sequences when typing special keys.

My target is calling iPXE and Grub as EFI applications. For navigation 
in Grub we need at least up, down, left, right, delete and F10. In 
lib/efi_loader/efi_console.c xterm escape sequences are translated to 
EFI scan codes.

Before the patch series the U-Boot USB keyboard driver signals up, down, 
left and right as non-standard character codes 0x6, 0x2, 0xe, 0x10. 
F1-F12, Insert, Delete, Home, End, Page Up, and Page Down are not supported.

Function cread_line() (in common/cli_readline.c) interprets both xterm 
escape sequences and non-standard control characters provided by the USB 
keyboard driver.

JinHua Luo's patch
Add readline cmdline-editing extension
501090aaa67b6072ebe8b721c8328d32be607660
which introduced command line editing unfortunately does not describe 
why it chose CTRL+B, CTRL+F, CTRL+N, and CTRL+P for navigation. These 
codes are not documented in any README.

> 
>> This preparatory patch changes function usb_kbd_put_queue() to allow adding
>> multiple characters at once. If the buffer cannot accommodate the whole
>> sequence, it is rejected completely.
>>
>> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
>> ---
>>   common/usb_kbd.c | 42 +++++++++++++++++++++++++-----------------
>>   1 file changed, 25 insertions(+), 17 deletions(-)
>>
>> diff --git a/common/usb_kbd.c b/common/usb_kbd.c
>> index 8cbdba6ac2..706cc350a6 100644
>> --- a/common/usb_kbd.c
>> +++ b/common/usb_kbd.c
>> @@ -125,24 +125,32 @@ extern int __maybe_unused net_busy_flag;
>>   /* The period of time between two calls of usb_kbd_testc(). */
>>   static unsigned long __maybe_unused kbd_testc_tms;
>>   
>> -/* Puts character in the queue and sets up the in and out pointer. */
>> -static void usb_kbd_put_queue(struct usb_kbd_pdata *data, char c)
>> +/*
>> + * Put characters into ring buffer.
>> + *
>> + * @data:	private data
>> + * @buf		buffer with data to be queued
>> + * @count:	number of characters to be queued
>> + */
>> +static void usb_kbd_put_queue(struct usb_kbd_pdata *data,
>> +			      uint8_t *buf, int count)
>>   {
>> -	if (data->usb_in_pointer == USB_KBD_BUFFER_LEN - 1) {
>> -		/* Check for buffer full. */
>> -		if (data->usb_out_pointer == 0)
>> -			return;
>> -
>> -		data->usb_in_pointer = 0;
>> -	} else {
>> -		/* Check for buffer full. */
>> -		if (data->usb_in_pointer == data->usb_out_pointer - 1)
>> -			return;
>> -
>> -		data->usb_in_pointer++;
>> +	int i, used;
>> +
>> +	/* Check if buffer holds at least 'count' free slots */
>> +	used = data->usb_in_pointer - data->usb_out_pointer;
>> +	if (used < 0)
>> +		used += USB_KBD_BUFFER_LEN;
>> +	if (used + count >= USB_KBD_BUFFER_LEN)
>> +		return;
>> +
>> +	/* Copy to buffer */
>> +	for (i = 0; i < count; ++i) {
>> +		++data->usb_in_pointer;
>> +		if (data->usb_in_pointer == USB_KBD_BUFFER_LEN)
>> +			data->usb_in_pointer = 0;
>> +		data->usb_kbd_buffer[data->usb_in_pointer] = buf[i];
> 
> memcpy() ?

Typically we copy only one byte. But escape sequences have maximum 
length are 8 bytes (e.g. CTRL+F8).

We have to consider the case with wrap around. This would require two 
memcpy() calls.

The coding would neither get faster in the average nor less complex 
using memcpy(). So let's keep it as it is.

Best regards

Heinrich

> 
>>   	}
>> -
>> -	data->usb_kbd_buffer[data->usb_in_pointer] = c;
>>   }
>>   
>>   /*
>> @@ -237,7 +245,7 @@ static int usb_kbd_translate(struct usb_kbd_pdata *data, unsigned char scancode,
>>   	/* Report keycode if any */
>>   	if (keycode) {
>>   		debug("%c", keycode);
>> -		usb_kbd_put_queue(data, keycode);
>> +		usb_kbd_put_queue(data, &keycode, 1);
>>   	}
>>   
>>   	return 0;
>>
> 
>